Imaging apparatus and focusing control method

ABSTRACT

Provided is an imaging apparatus capable of performing AF with a high precision regardless of an object while realizing increase in AF speed. When there is an AF instruction, photographing is performed while a focus lens is moved. AF evaluated values are calculated at every position of the focus lens by a contrast AF processing unit. The contrast AF processing unit calculates a sharpness in the vicinity of the maximal point of an evaluated value curve from three AF evaluated values, including the maximum value among calculated AF evaluated values and AF evaluated values calculated at positions in front and rear of a focus lens position corresponding to the maximum value, and position information of the focus lens corresponding thereto, and calculates a focusing position by a calculation method selected from among plural kinds of methods according to the sharpness.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of copending application Ser. No.14/825,678 filed on Aug. 13, 2015, which is a continuation ofInternational Application No. PCT/JP2013/079888 filed on Nov. 5, 2013,and claims priority from Japanese Patent Application No. 2013-026862,filed on Feb. 14, 2013, the entire contents of all of which areexpressly incorporated by reference into the present application.

BACKGROUND

1. Technical Field

The present invention relates to an imaging apparatus having anauto-focus function.

2. Related Art

Recently, as the high resolution of a solid imaging element such as aCMOS (Charge Coupled Device image sensor or a CMOS (Complementary MetalOxide Semiconductor image sensor has been attained, a demand forinformation devices having a photographing function such as a digitalstill camera, a digital video camera, a cellular phone (e.g., a smartphone), and a personal digital assistant (PDA) is rapidly increasing.Meanwhile, information appliances having an imaging function asdescribed above are referred to as imaging apparatuses.

The imaging apparatuses employ a contrast auto-focus (AF) method or aphase difference AF method as a focusing control method for focusing ona main object.

The contrast AF method is a method for acquiring a picked-up imagecontrast, obtained in each driving step, as an evaluated value whilemoving a focus lens in the optical axis direction, and setting a lensposition having the highest evaluated value as a focusing position.

Here, the focus lens refers to a lens that moves in the optical axisdirection to adjust the focal distance of a photographing opticalsystem. In a lens unit including a plurality of lenses, the focus lensindicates a lens that adjusts a focal position. In the case where theentire group of lenses extends, the focus lens indicates all the entiregroup.

There are various methods for determining a lens position having themaximum evaluated value. For example, Patent Literature 1(JP-A-2005-345695) discloses a method for calculating a lens position(focusing position) corresponding to a maximal point of an evaluatedvalue curve by performing a so-called three-point interpolationcalculation with respect to three points (a plotted point P2 of themaximum value (the maximum evaluated value) among obtained evaluatedvalues, a plotted point P1 of an evaluated value obtained before themaximum evaluated value, and a plotted point P3 of an evaluated valueobtained after the maximum evaluated value) in a graph in which thehorizontal axis represents a lens position and the vertical axisrepresents an evaluated value. Specifically, the focusing position isobtained from an intersection between a straight line that passesthrough the point P2 and the point P3 and has a gradient of a and astraight line that passes through the point P1 and has a gradient of —α.

In addition, Patent Literature 2 (2004-279721) discloses a method fordetermining a function of a curve passing through the three points andcalculating a lens position corresponding to a maximal point of anevaluated value curve from the function. A spline function or a Bezierfunction is used as the function.

SUMMARY OF INVENTION

The method disclosed in Patent Literature 2 is capable of determining afocusing position having a small error when the vicinity of the maximalpoint of a real evaluated value curve has a gently sloping mountainshape. In addition, the method is advantageous in increasing an AF speedbecause it enables calculation of the focusing position with a highprecision even if the sampling number of evaluated values is small.

However, some photographed objects may have a steep mountain shape inthe vicinity of the maximal point of the evaluated value curve. Forexample, in a landscape scene including a tree with many leaves, thevicinity of the maximal point of the evaluated value curve has a steepmountain shape because the frequency band of an image approaches a highfrequency side. In particular, since many recent imaging apparatuses areequipped with a wide-angle lens, the vicinity of the maximal point ofthe evaluated value curve is easy to become steep by the influence ofthe wide-angle lens. In addition, in a recent camera, the vicinity ofthe maximal point of the evaluated value curve tends to easily becomesteep because the brightness of a lens increases.

As described above, when the vicinity of the maximal point of theevaluated value curve has a steep mountain shape, the evaluated valuecurve may be considerably different from an assumed curve shape in themethod for estimating the maximal point of the evaluated value curve bythe function of the curve as described in Patent Literature 2.Therefore, an error in obtained focusing position increases.

The method for obtaining a focusing position using the gradients ofstraight lines as described in Patent Literature 1 may obtain a focusingposition with a certain precision regardless of the shape of theevaluated value curve. However, this method tends to exhibit anincreased error as the sampling number of evaluated values decreases inorder to improve an AF speed.

In view of above, illustrative aspects of the present invention is toprovide an imaging apparatus and a focusing control method which arecapable of performing AF with a high precision regardless of aphotographed object.

An aspect of the present invention provides an imaging apparatusincluding: a focus lens configured to be movable in an optical axisdirection; an imaging element configured to image an object via thefocus lens; an evaluated value calculation unit configured to calculatean evaluated value for focusing using a picked-up image signal obtainedthrough imaging by the imaging element at every position of the focuslens while moving the focus lens; a sharpness calculation unitconfigured to calculate a sharpness in a vicinity of a maximal point ofan evaluated value curve, which represents relationship between aposition of the focus lens and the evaluated value, using at least threeevaluated values calculated by the evaluated value calculation unit andposition information of the focus lens corresponding to each of thethree evaluated values; a focusing position calculation unit configuredto select, according to at least the sharpness calculated by thesharpness calculation unit, one of plural kinds of calculation methodsusing the three evaluated values and the position information of thefocus lens corresponding to each of the three evaluated values, and tocalculate the position of the focus lens corresponding to the maximalpoint of the evaluated value curve as a focusing position using theselected calculation method; and a focusing control unit configured toperform a focusing control to move the focus lens to the focusingposition, in which the calculation methods include: a first calculationmethod for calculating a second or higher degree function representingthe evaluated value curve using the three evaluated values and theposition information of the focus lens corresponding to each of thethree evaluated values, and calculating the focusing position using thesecond or higher degree function; and a second calculation method forcalculating a first degree function using the three evaluated values andthe position information of the focus lens corresponding to each of thethree evaluated values and calculating the focusing position using thefirst degree function, and in which the three evaluated values include amaximum value among the evaluated values calculated by the evaluatedvalue calculation unit and evaluated values calculated in relation withpositions in front and rear of the position of the focus lenscorresponding to the maximum value.

Another aspect of the present invention provides a focusing controlmethod by an imaging apparatus having an imaging element configured toperform imaging of an object via a focus lens that is movable in anoptical axis direction, the method including: an evaluated valuecalculation step of calculating an evaluated value for focusing using apicked-up image signal obtained through imaging by the imaging elementat every position of the focus lens while moving the focus lens; asharpness calculation step of calculating a sharpness in a vicinity of amaximal point of an evaluated value curve, which represents relationshipbetween a position of the focus lens and the evaluated value, using atleast three evaluated values calculated by the evaluated valuecalculation unit and position information of the focus lenscorresponding to each of the three evaluated values; a focusing positioncalculation step of selecting, according to at least the sharpnesscalculated by the sharpness calculation unit, one of plural kinds ofcalculation methods using the three evaluated values and the positioninformation of the focus lens corresponding to each of the threeevaluated values, and calculating the position of the focus lenscorresponding to the maximal point of the evaluated value curve as afocusing position using the selected calculation method; and a focusingcontrol step of performing a focusing control to move the focus lens tothe focusing position, in which the calculation methods include: a firstcalculation method for calculating a second or higher degree functionrepresenting the evaluated value curve using the three evaluated valuesand the position information of the focus lens corresponding to each ofthe three evaluated values, and calculating the focusing position usingthe second or higher degree function; and a second calculation methodfor calculating a first degree function using the three evaluated valuesand the position information of the focus lens corresponding to each ofthe three evaluated values and calculating the focusing position usingthe first degree function, and in which the three evaluated valuesinclude a maximum value among the evaluated values calculated by theevaluated value calculation unit and evaluated values calculated inrelation with positions in front and rear of the position of the focuslens corresponding to the maximum value.

According to any one of the aspects of the present invention, it ispossible to provide an imaging apparatus and a focusing control methodwhich are capable of performing AF with a high precision regardless of aphotographing object.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a schematic configuration of a digitalcamera as one example of an imaging apparatus for explaining anexemplary embodiment of the present invention.

FIG. 2 is a functional block diagram of a contrast AF processing unit 19in the digital camera illustrated in FIG. 1.

FIG. 3 is a view illustrating one example of an AF evaluated valuecurve.

FIG. 4 is a view illustrating one example of an AF evaluated valuecurve.

FIG. 5 is a view for explaining calculation errors of a focusingposition by a first calculation method and a second calculation methodin a case where the AF evaluated value curve is as illustrated in FIG.4.

FIG. 6 is a flowchart for explaining an AF operation of the digitalcamera illustrated in FIG. 1.

FIG. 7 is a flowchart for explaining one variation of the AF operationof the digital camera illustrated in FIG. 1.

FIG. 8 is a flowchart for explaining another variation of.the AFoperation of the digital camera illustrated in FIG. 1.

FIG. 9 is a view explaining a smart phone serving as an imagingapparatus.

FIG. 10 is an internal block diagram of the smart phone of FIG. 9.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the drawings.

FIG. 1 is a view illustrating a schematic configuration of a digitalcamera as one example of an imaging apparatus for explaining anexemplary embodiment of the present invention.

An imaging system of the digital camera illustrated in FIG. 1 includesan imaging optical system (including a photographing lens 1 and an iris2) and a solid imaging element 5 such as a CCD type or CMOS typeelement. The imaging optical system including the photographing lens 1and the iris 2 is removably coupled or fixed to a camera main body. Thephotographing lens 1 includes a focus lens that is movable in theoptical axis direction. The solid imaging element 5 is not equipped withan optical low-pass filter and, thus achieves a high resolution.

A system control unit 11 that totally controls the entire electriccontrol system of the digital camera controls a flash light emittingunit 12 and a light receiving unit 13. In addition, the system controlunit 11 controls a lens drive unit 8 so as to adjust the position of thefocus lens included in the photographing lens 1. In addition, the systemcontrol unit 11 controls the opening degree of the iris 2 through aniris drive unit 9, thereby adjusting the quantity of exposure.

In addition, the system control unit 11 drives the solid imaging element5 via an imaging element drive unit 10 and outputs, as a picked-up imagesignal, an object image obtained via the photographing lens 1. Aninstruction signal is input by a user to the system control unit 11 viaan operating unit 14.

In addition, the electric control system of the digital camera includesan analog signal processing unit 6 that performs an analog signalprocessing such as a correlative double sampling processing connected toan output of the solid imaging element 5, and an ND conversion circuit 7that converts an analog signal, output from the analog signal processingunit 6, into a digital signal. The analog signal processing unit 6 andthe A/D conversion circuit 7 are controlled by the system control unit11. The analog signal processing unit 6 and the A/D conversion circuit 7may be mounted in the solid imaging element 5.

In addition, the electric control system of the digital camera includesa main memory 16, a memory control unit 15 connected to the main memory16, a digital signal processing unit 17 that produces photographed imagedata by performing, for example, an interpolation calculation, a gammarevision calculation, and an RGB/YC conversion processing on a picked-upimage signal output from the A/D conversion circuit 7, acompression/extension processing unit 18 that compresses image dataproduced in the digital signal processing unit 17 in a JPEG form orextends compressed image data, a contrast AF processing unit 19, anexternal memory control unit 20 connected to a freely removablerecording medium 21, and a display control unit 22 connected to adisplay unit 23 that is mounted to, for example, the rear surface of thecamera. The memory control unit 15, the digital signal processing unit17, the compression/extension processing unit 18, the contrast AFprocessing unit 19, the external memory control unit 20, and the displaycontrol unit 22 are connected to one another via a control bus 24 and adata bus 25, and are controlled by a command from the system controlunit 11.

FIG. 2 is a functional block diagram of the contrast AF processing unit19 in the digital camera illustrated in FIG. 1.

The contrast AF processing unit 19 includes an AF evaluated valuecalculation unit 191, a sharpness calculation unit 192, and a focusingposition calculation unit 193. These functional blocks are formed as aprocessor included in the system control unit11 executes a program.

The AF evaluated value calculation unit 191 calculates an AF evaluatedvalue for focusing using a picked-up image signal obtained via imagingusing the solid imaging element 5 at every moved position (at three ormore positions) while moving the focus lens position of the imaging lens1 under the control of the system control unit 11. The AF evaluatedvalue is obtained, for example, by multiplying brightness differencesbetween neighboring respective pixels (photoelectric conversionelements) of the solid imaging element 5. Alternatively, the AFevaluated value may be obtained by extracting high frequency componentsof an image output from the imaging element using a high frequencytransmission filter and multiplying the extracted high frequencycomponents.

The sharpness calculation unit 192 calculates the sharpness in thevicinity of the maximal point of the evaluated value curve (a pointwhere an evaluated value becomes the maximum), which represents therelationship between the focus lens position and the AF evaluated valuefor an object that is being photographed, using at least three AFevaluated values, including the maximum value among AF evaluated valuescalculated by the AF evaluated value calculation unit 191 and two AFevaluated values calculated in relation to positions in front and rearof the focus lens position corresponding to the maximum AF evaluatedvalue, and the focus lens position information corresponding to each ofthe three AF evaluated values.

FIGS. 3 and 4 are views illustrating examples of evaluated value curves.When an object in a desired focusing region (AF region) is dominant inlow frequency component, the evaluated value curve becomes an evaluatedvalue curve 30 having a low sharpness in the vicinity of the maximalpoint, as illustrated in FIG. 3. Meanwhile, when the object in the AFregion is dominant in high frequency component the evaluated value curvebecomes an evaluated value curve 40 having a high sharpness in thevicinity of the maximal point, as illustrated in FIG. 4.

As described above, the evaluated value curve has a sharpness varied inthe vicinity of the maximal point depending on an object. The sharpnesscalculation unit 192 calculates the sharpness that varies by adifference in object.

Hereinafter, a sharpness calculation method will be described.

FIG. 3 illustrates at least three AF evaluated values y0, y1 and y2 asdescribed above and focus lens position information x0, x1, and x2corresponding to the respective three AF evaluated values. The AFevaluated value y1 is the maximum value among the AF evaluated valuescalculated by the AF evaluated value calculation unit 191.

The sharpness calculation unit 192 calculates a sharpness S that is anindex representing the sharpness in the vicinity of the maximal point ofthe evaluated value curve.

When the relationship between the three AF evaluated values y0, y1, andy2 and the focus lens positions x0, x1, and x2 corresponding thereto isrepresented by, for example, a second degree function, an approximatefunction is assumed as follows;

y=c0+c1(x−x0)+c2(x−x0)(x−x1) . . .   (1)

In Formula (1), “c2” is obtained using, for example, a well-knownNewtonian interpolation method.

When substituting x=x0 and y=y0 into Formula (1), the following may beobtained.

y0=c0 . . .   (2)

When substituting x=x1 and y=y1 into Formula (1), the following may beobtained.

y1=c0+c1(x1−x0) . . .   (3)

When subtracting Formula (2) from Formula 3, y1−y0=c1(x1−x0) and fromthe formula, c1=(y1−y0)/(x1−x0).

When substituting x=x2 and y=y2 into Formula (1), the following may beobtained.

y2=c0+c1(x2−x0)+c2(x2−x0)(x2−x1) . . .   (4)

When subtracting Formula (3) from Formula (4), y2−y1=c1(x2−x1)+c2(x2−x0)(x2−x1)={c1+c2(x2−x0)}(x2−x1) is obtained which is also expressed asc2={(y2−y1)/(x2−x1)−c1}/(x2−x0).

While “c2” has a minus value because the parabola of AF evaluated valuesis upwardly convex, the sharpness is determined based on an absolutevalue of c2 in order to simplify the description.

In a case where the absolute value of C2 is large, the approximatefunction of AF evaluated values becomes a steep parabola because theparabola is more greatly varied in y with respect to the variation in x.

Because sampling points of AF evaluated values are only three points,the value of c2 calculated by the method as described above may besignificantly different from the original sharpness. This is because thesampling points deviate from an approximate second degree curve.

For example, in a case where the maximum AF evaluated value among thethree points is y1 and y1 greatly deviates from an original value by acertain influence, c2 may deviate from the original curve to thedirection in which the sharpness is large in the form of being drawn toy1. Likewise, in a case where the two points x0 and x2 among thesampling points of AF evaluated values except for the maximum valuegreatly deviate in the x-axis direction, the absolute value of c2decreases in appearance.

In order to correct this, the inventor has found that{|x1−x0|×|x1−x2|}/y1 may be used as a coefficient of normalization, avalue obtained by multiplying the coefficient by c2 may be evaluated asthe sharpness S.

Here, AF evaluated values are taken at the three points x0, x1, and x2(x0<x1<x2), and the AF evaluated values are taken such that the AFevaluated value y1 at x1 becomes the maximum among y0, y1, and y2.

That is, the sharpness is evaluated as follows.

S={|c2|×|x1−x0|×x1−x2|}/y1 . . .   (5)

When this index is used, the sharpness may be more accurately determinedbecause the spreading state of the parabola may be determined based ononly one variable even if the magnitudes of the AF evaluated values orthe intervals between the sampling points are different from each other.

Alternatively, instead of the sharpness S, the sharpness calculationunit 192 calculates a distortion degree, skew, to be described below,which represents asymmetricity of opposite sides near an average valueof data distribution, as an index representing the sharpness in thevicinity of the maximal point of the evaluated value curve.

In a case of calculating the distortion degree, skew, by using at leasttwo AF evaluated values in addition to the three AF evaluated values asdescribed above, the x coordinate of the focus lens positioncorresponding to the maximum AF evaluated value is treated as zero. Inthis way, the distortion degree, skew, may be obtained by the followingFormula 6.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\{{skew} = {\frac{n}{\left( {n - 1} \right)\left( {n - 2} \right)}{\sum\limits_{i = 1}^{n}\; \left( \frac{x_{i} - \mu}{\delta} \right)^{3}}}} & (6)\end{matrix}$

In Formula (6), “n” is the number of AF evaluated values used incalculation and has a minimum value of 5. Xi of Formula (6) is a valuerepresenting the position of the focus lens, and, among X1 to Xn, Xi iszero when the AF evaluated value becomes the maximum. In addition, “μ”of Formula (6) is an average value of n AF evaluated values, and “δ” isa standard deviation of n AF evaluated values.

Among plural kinds of calculation methods using the three AF evaluatedvalues y0, y1, and y2 as described above and the focus lens positioninformation x0, x1 and x2 corresponding to the respective three AFevaluated values, the focusing position calculation unit 193 selects onemethod based on the sharpness calculated by the sharpness calculationunit 192 and calculates, as a focusing position, a focus lens positioncorresponding to the maximal point of the evaluated value curve usingthe selected calculation method.

The plural kinds of calculation methods include a first calculationmethod and a second calculation method.

The first calculation method is a method for calculating a second degreefunction that represents an evaluated value curve passing through threepoints (x0, x1), (x1, y1), and (x2, y2) and calculating a focusingposition using the calculated second degree function.

When the focusing position is calculated using the first calculationmethod, the focusing position calculation unit 193 assumes that anexpected evaluated value curve is a left-right symmetrical parabolay=ax²+βx+γ. In addition, the focusing position calculation unit 193 setsup simultaneous equations of a parabola passing through three points(x0, y0), (x1, y1), and (x2, y2) and solves the equations, therebyobtaining coefficients α, β, and γ of the second degree function showingthe parabola. Then, the obtained second degree function isdifferentiated to calculate an inflection point of the parabola(corresponding to the maximal point of the evaluated value curve) andhence to calculate a focusing position.

The second calculation method is a method for calculating a linearfunction passing through two points among the points (x0, y0), (x1, y1),and (x2, y2) and a linear function passing through the other point, boththe linear functions having plus and minus signs of the gradientsthereof, and calculating a focusing position using the two calculatedlinear functions.

When calculating the focusing position using the second calculationmethod, the focusing position calculation unit 193 first calculates alinear function representing a straight line (reference numeral 31 inFIG. 3) passing through (x0, y0) and (x1, y1) and a linear functionrepresenting a straight line (reference numeral 32 in FIG. 3) passingthrough (x1, y1) and (x2, y2).

Then, by comparing the magnitudes of gradients (absolute values except asign) of the two linear functions, the focusing position calculationunit 193 calculates a linear function, which has the plus/minus sign ofthe gradient opposite to that of the linear function having the greatergradient (the linear function represented by the straight line 31 in theexample of FIG. 3) and represents a straight line (reference numeral 33in FIG. 3) passing through the other point (x2, y2) other than the twopoints through which the straight line having the greater gradientpasses.

Finally, the focusing position calculation unit 193 calculates, as afocusing position, the x coordinate (xg in FIG. 3) at the intersectionof the straight line 31 and the straight line 33 using the linerfunctions representing the straight line 31 and the straight line 33.

The first calculation method is advantageous in increasing the AF speedbecause the AF precision may be maintained even if the sampling numberof AF evaluated values decreases. However, when a real evaluated valuecurve has an increased sharpness in the vicinity of the maximal point asillustrated in FIG. 4, an error in the calculated focusing positionincreases.

Meanwhile, in a case where the evaluated value curve was as illustratedin FIG. 4, the second calculation method may reduce an error in thecalculated focusing position as compared to the case in which the firstcalculation method is used.

FIG. 5 is a view illustrating a focusing position x(1) calculated by thefirst calculation method and a focusing position x(2) calculated by thesecond calculation method in a case where the evaluated curve is theevaluated value curve illustrated in FIG. 4. As illustrated in FIG. 5,in a case where the evaluated value curve has a high sharpness, thefocusing position obtained by the second calculation method comes closerto an accurate value. The result illustrated in FIG. 5 is given by wayof example and the calculated results of the focusing positions by thefirst calculation method and the second calculation method may increase.In addition, the second calculation method may be used because focusdeviation has an effect on image quality even at a difference asillustrated in FIG. 5.

Accordingly, the focusing position calculation unit 193 calculates afocusing position by the first calculation method in a case where thesharpness calculated by the sharpness calculation unit 192 is equal toor less than a predetermined critical value TH1, and calculates afocusing position by the second calculation method having a smallererror in a case where the sharpness calculated by the sharpnesscalculation unit 192 exceeds the predetermined critical value TH1. Thatis, the focusing position calculation unit 193 selects a calculationmethod having a smaller error according to the sharpness and calculatesa focusing position by the selected method, thereby preventingdeterioration in AF precision.

Next, an AF operation of the digital camera illustrated in FIG. 1 willbe described.

FIG. 6 is a flowchart for explaining an AF operation of the digitalcamera illustrated in FIG. 1. The flowchart illustrated in FIG. 6 beginsas a shutter button is half-pushed or an instruction to perform AF isinput to the system control unit 11.

When there is an instruction to perform AF, the system control unit 11moves the focus lens from a MOD stage to an INF stage. While the focuslens is moving, imaging is performed by the solid imaging element 5 atevery prescribed time and picked-up image signals obtained by theimaging are transmitted to the contrast AF processing unit 19.

The contrast AF processing unit 19 calculates AF evaluated values fromthe obtained picked-up image signals whenever the picked-up imagesignals are obtained, and stores, in the main memory 16, positioninformation of the focus lens when the picked-up image signals areobtainable such that the position information corresponds to thecalculated AF evaluated values (step S1).

The sharpness calculation unit 192 obtains, from the main memory 16,peak point data that includes the maximum AF evaluated value and thefocus lens position information corresponding thereto, pre-peak pointdata that includes position information in front of the focus lensposition (the MOD stage side or the INF stage side) and an AF evaluatedvalue corresponding thereto, and post-peak point data that includesposition information behind the focus lens position (at the INF stageside or the MOD stage side) and an AF evaluated value correspondingthereto by monitoring the AF evaluated values stored in the main memory16. Then, the sharpness calculation unit 192 calculates the sharpness inthe vicinity of the maximal point of the evaluated value curve using theobtained pre-peak point data, peak point data, and post-peak point data(step S2).

The focusing position calculation unit 193 compares the sharpnesscalculated in step S2 with a critical value TH1 (step S3). When thesharpness is equal to or less than the critical value TH1 (step S3: NO),the focusing position calculation unit 193 calculates a focusingposition by the first calculation method using the pre-peak point data,the peak point data, and the post-peak point data (step S4).

Meanwhile, when the sharpness exceeds the critical value TH1 (step S3:YES), the focusing position calculation unit 193 calculates a focusingposition by the second calculation method using the pre-peak point data,the peak point data, and the post-peak point data (step S5).

When the focusing position is calculated in steps S4 and S5, the systemcontrol unit 11 controls the movement of the focus lens to the focusingposition based on the calculated focusing position information (stepS6), and terminates the auto-focus processing.

As described above, according to the digital camera of FIG. 1, thesharpness in the vicinity of the maximal point of an evaluated valuecurve that obtained by calculating AF evaluated values at each of aplurality of focus lens positions is estimated by at least three pointdata and a focusing position is calculated based on the sharpness usinga calculation method having a smaller error. Thus, the AF precision maybe improved as compared to a conventional method for calculating afocusing position using only a first calculation method or a secondcalculation method.

In addition, according to the digital camera of FIG. 1, the sharpnessmay be calculated when there are at least three point data and the AFprecision may be improved by switching between the calculation methodsbased on the sharpness. Therefore, it is unnecessary to improve the AFprecision by reducing the movement speed of the focus lens to increasethe sampling number of AF evaluated values. Accordingly, the increasedAF speed and the improved AF precision may be accomplished.

Meanwhile, in the above description, a curve function used in the firstcalculation method is a second degree function showing a right-rightsymmetrical parabola. However, in a case where so-called panning isperformed in which photographing is performed by focusing on an objectwhile following the moving object, the evaluated value curve may not beleft-right symmetrical by the movement speed of the object.

Thus, in a case where the first calculation method is selected, afocusing position may be calculated using a second function as well as ahigher degree function (e.g., a spline curve function or a Bezier curvefunction) as a curve function.

When using a third or higher degree function, the function is calculatedby obtaining point data of the number according to the degree from themain memory 16. In addition, in a case of selecting the firstcalculation method, which function will be used may be determined basedon the speed of a moving object which is detected by an imageprocessing, or the movement speed of the digital camera detected using amovement detector such as a gyroscope sensor.

In addition, in a case where the first calculation method is selected,when using a second degree function as a curve function, a focusingposition may be calculated to reduce a calculation error of the focusingposition after a processing of displacing the phase of a parabolapassing through a pre-peak point, a peak point, and a post-peak point isperformed using separate point data other than the pre-peak point data,the peak point data, and the post-peak point data.

Hereinafter, a variation of the AF operation of the digital cameraillustrated in FIG. 1 will be described.

FIG. 7 is a flowchart for explaining one variation of the AF operationof the digital camera illustrated in FIG. 1. The flowchart illustratedin FIG. 7 is identical to the flowchart illustrated in FIG. 6 exceptthat step S10. The processings of FIG. 7, which are the same as theprocessings illustrated in FIG. 6, will be designated by the samereference numerals and descriptions thereof will be omitted.

The sharpness calculation unit 192 estimates the sharpness from at leastthree point data. Therefore, in a case where much noise enters in AFevaluated values included in the point data, the reliability of thecalculated sharpness is deteriorated. In addition, when much noise isincluded in the AF evaluated values, the second calculation method has agreater error than the first calculation method.

For example, in a case where the photographing environment is a darkplace, the influence of noise increases. Examples of noise quantitymeasurement methods include a method in which variation in thebrightness of a live view image is handled as the noise quantity, amethod in which variation in AF evaluated value obtained from a liveview image is handled as the noise quantity, and a method in whichresults of AF evaluated values (difference in the forms of the evaluatedvalues) are compared and determined through a plurality of filtershaving different bands.

As such, in this variation, when the determination of step S3 is YES,the focusing position calculation unit 193 determines the noise quantityincluded in the AF evaluated values calculated in step S1 (step S10).When the noise quantity exceeds a critical value TH2, the focusingposition calculation unit 193 performs the processing of step S4, andwhen the noise quantity is equal to or less than the critical value TH2,the focusing position calculation unit 193 performs the processing ofstep S5.

The noise quantity included in the AF evaluated values increases in asituation in which the brightness of an object is low and an analog gainof a picked up image signal increases (upon setting of high ISOsensitivity). In addition, the noise quantity included in the AFevaluated values increases even in a situation where hand shakingoccurs.

The focusing position calculation unit 193 determines whether or not thenoise quantity included in the AF evaluated values exceeds the criticalvalue TH2 by the brightness of the object, the magnitude of ISOsensitivity, or existence or non-existence of occurrence of handshaking. When the noise quantity exceeds the critical value TH2, thefocusing position calculation unit 193 determines that the reliabilityof the sharpness calculated by the sharpness calculation unit 192 islow. Thus, even if the sampling number is small, the focusing positioncalculation unit 193 may calculate the focusing position with a highprecision even if the sampling number is low, and even if the noise ismuch, the focusing position calculation unit 193 calculates the focusingposition by the first calculation method having a smaller error.

In this way, even though the real evaluated value curve is asillustrated in FIG. 3, the second calculation method having a greatererror is employed, which may prevent degradation of the AF precision.

FIG. 8 is a flowchart for explaining another variation of the AFoperation of the digital camera illustrated in FIG. 1. The flowchartillustrated in FIG. 8 is identical to the flowchart illustrated in FIG.6 except that steps S11, S12 and S13 are added. In FIG. 8, theprocessings which are the same as those illustrated in FIG. 6 will bedesignated by the same reference numerals and descriptions thereof willbe omitted.

In a case where panning is being performed, when the movement speed ofan object (the same meaning as the movement speed of the camerafollowing the object) is great, the evaluated value curve does not havea left-right symmetrical shape. As such, in a photographing situationwhere the evaluated value curve has a left-right asymmetrical shape, theerror in the case where the focusing position is calculated using athird or higher degree function such as a spline curve function or aBezier curve function is smaller than the error in the case where thefocusing position is calculated using a second degree function or afirst degree function.

For this reason, after step S1, the system control unit 11 determineswhether or not panning is being performed (step S11).

The system control unit 11 determines whether or not panning isperformed by detecting movement of the camera using detectioninformation from a movement detector such as a gyroscope sensorinstalled to the digital camera, detecting that the object that is beingphotographed includes a moving object by analyzing a live view image, orvia a combination thereof.

When panning is not performed, the processings after step S2 areperformed.

Meanwhile, when panning was performed, the system control unit 11compares the movement speed of the camera detected by the movementdetector or the movement speed of the moving object detected by analysisof the live view image with a predetermined critical value TH3 (stepS12).

When the movement speed of the camera or the movement speed of themoving object is equal to or less than the critical value TH3, theprocessings after step S2 are performed. When the movement speed of thecamera or the movement speed of the moving object exceeds the criticalvalue TH3, the processing of step S13 is performed.

In step S13, the focusing position calculation unit 193 calculates athird or higher degree function such as a spline curve function or aBezier curve function from the evaluated values calculated in step S1and the focus lens position information corresponding thereto and thencalculates a focusing position using the calculated function. Theprocessing of step S6 is performed after step S13.

As described above, according to the digital camera of the presentvariation, in a situation where the panning is being performed and themovement speed of the camera or the moving object is high, i.e. in asituation where the evaluated value curve is left-right asymmetrical,the AF processing may be efficiently performed with a high precisionbecause the focusing position is calculated using a high degree curvefunction of third or higher degree without calculating the sharpness.

Meanwhile, in FIG. 8, after step S2, step S10 may be added in the samemanner as in FIG. 7.

Heretofore, descriptions have been made assuming that the solid imagingelement 5 is not equipped with an optical loss-pass filter. Because thesolid imaging element not equipped with an optical loss-pass filter hasan increased resolution as compared to a solid imaging element equippedwith an optical loss-pass filter, high frequency components in aphotographed image increase. For this reason, the solid imaging elementnot equipped with an optical loss-pass filter strongly tends to attainan evaluated value curve having a high sharpness as illustrated in FIG.4. Thus, employing the AF control described in the present exemplaryembodiment is particularly effective.

Even with a solid imaging element equipped with an optical loss-passfilter, the evaluated value curve may have a high sharpness in someobjects as illustrated in FIG. 4. Therefore, even in a case where asolid imaging element equipped with an optical loss-pass filter is usedas the solid imaging element 5, employing the AF control described inthe present exemplary embodiment is effective.

Subsequently, descriptions will be made on a configuration of a smartphone serving as an imaging apparatus.

FIG. 9 illustrates an external appearance of a smart phone 200 as anexemplary embodiment of the imaging apparatus of the present invention.The smart phone 200 illustrated in FIG. 9 includes a housing 201 havinga flat plate shape, and is provided with a display panel 202 serving asa display unit one surface of the housing 201, and a display input unit204 having an operating panel 203 serving as an input unit which isintegrally formed therewith. In addition, the housing 201 includes aspeaker 205, a microphone 206, an operating unit 207, and a camera unit208. Meanwhile, the configuration of the housing 201 is not limitedthereto, and may employ, for example, a configuration in which a displayunit and an input unit are independent from each other, or aconfiguration having a folder structure or a slide mechanism.

FIG. 10 is a block diagram illustrating a configuration of the smartphone 200 illustrated in FIG. 9. As illustrated in FIG. 9, the smartphone 200 includes, as major components, a wireless communication unit210, a display input unit 204, a call unit 211, an operating unit 207, acamera unit 208, a storage unit 212, an external input/output unit 213,a GPS (Global Positioning System) receiver unit 214, a motion sensorunit 215, a power source unit 216, and a main control unit 220. Inaddition, the smart phone 200 is provided with, as a major function, awireless communication function for mobile wireless communication with abase station BS (not illustrated) through a mobile communication network(NW) (not illustrated).

The wireless communication unit 210 performs wireless communication withthe base station BS accommodated in the mobile communication network NWaccording to an instruction of the main control unit 220. The wirelesscommunication unit 210 performs transmission/reception of, for example,various file data such as voice data and image data, and electronic maildata, or reception of, for example, web data or streaming data using thewireless communication.

The display input unit 204 is a so-called touch panel that displays, forexample, images (still images and moving images) or text information soas to visually transmit the information to a user under the control ofthe main control unit 220 and to detect the user's operation withrespect to the displayed information, and is provided with a displaypanel 202 and an operating panel 203.

The display panel 202 uses, for example, an LCD (Liquid Crystal Display)or an OLED (Organic Electro-Luminescence Display) serving as a displaydevice.

The operating panel 203 is a device that is disposed on a displaysurface of the display panel 202 so as to enable visual recognition ofan image displayed on the display surface and to detect one or morecoordinates operated by the user's fingers or a stylus. When the deviceis operated by the user's fingers or the stylus, the operating panel 203outputs a detection signal generated due to the operation to the maincontrol unit 220. Subsequently, the main control unit 220 detects anoperating position (coordinates) on the display panel 202 based on thereceived detection signal.

As illustrated in FIG. 9, the display panel 202 and the operating panel203 of the smart phone 200 exemplified as one exemplary embodiment of animaging apparatus of the present invention are integrally formed toconstitute the display input unit 204. The operating panel 203 isarranged to completely cover the display panel 202.

When this arrangement is employed, the operating panel 203 may have afunction of detecting the user's operation even with respect to a regionoutside the display panel 202. In other words, the operating panel 203may have a detection region (hereinafter, referred to as a displayregion) related to an overlapping portion that is superposed on thedisplay panel 202, and the remaining detection region (hereinafter,referred to as a non-display region) related to an outer edge portionthat is not superposed on the display panel 202.

Meanwhile, the size of the display region and the size of the displaypanel 202 may be completely matched to each other, but it is not alwaysnecessary to match both sizes with each other. In addition, theoperating panel 203 may have two sensitive regions of an outer edgeportion and an inner portion other than the outer edge portion. Inaddition, the width of the outer edge portion is appropriately designedaccording to, for example, the size of the housing 201. In addition, aposition detection method employed in the operating panel 203 may be,for example, a matrix switch method, a resistance film method, a surfaceelastic wave method, an infrared method, an electronic induction method,and a capacitance method, and any method may be employed.

The call unit 211 includes the speaker 205 or the microphone 206 so asto convert the user's voice input through the microphone 206 into voicedata processable by the main control unit 220 and output the voice datato the main control unit 220, or to decode voice data received by thewireless communication unit 210 or the external input/output unit 213and output the decoded voice data from the speaker 205. In addition, asillustrated in FIG. 9, for example, the speaker 205 may be mounted onthe same surface as the installation surface of the display input unit204, and the microphone 206 may be mounted to a side surface of thehousing 201.

The operating unit 207 is a hardware key using, for example, a keyswitch and receives an instruction from the user. For example, asillustrated in FIG. 9, the operating unit 207 is mounted on the sidesurface of the housing 201 of the smart phone 200. The operating unit207 is a push button type switch that is turned on when pushed by, forexample, a finger and turned off by restoration of, for example, aspring when the finger is removed.

The storage unit 212 stores control programs or control data of the maincontrol unit 220, application software, address data corresponding to,for example, the name or phone number of a communication partner, dataof transmitted/received e-mails, and web data downloaded by web browsingor downloaded content data, and temporarily stores, for example,streaming data. In addition, the storage unit 212 is configured by aninternal storage unit 217 embedded in the smart phone and an externalstorage unit 218 having a freely separable external memory slot.Meanwhile, each of the internal storage unit 217 and the externalstorage unit 218 constituting the storage unit 212 is implemented usinga storage medium such as a flash memory type memory, a hard disk typememory, a multimedia card micro type memory, a card type memory (e.g., aMicroSD (registered trademark) memory), a RAM (Random Access Memory), ora ROM (Read Only Memory.

The external input/output unit 213 serves as an interface with allexternal appliances connected to the smart phone 200 and is intended tobe directly or indirectly connected to other external appliances viacommunication (e.g., universal serial bus or IEEE1394) or network (e.g.,Internet, wireless LAN, Bluetooth (registered trademark), RFID (RadioFrequency IDentification), infrared data association (IrDA) (registeredtrademark), ultra wide band (UWB) (registered mark), and ZigBee(registered trademark)).

Examples of external appliances connected to the smart phone 200 includea wired/wireless headset, a wired/wireless external charger, awired/wireless data port, a memory card connected via a card socket, aSIM (Subscriber Identity Module) card/UIM (User Identity Module) card,an external audio/video appliance connected via an audio/video I/O(Input/Output) terminal, a wirelessly connected external audio/videoappliance, a wiredly/wirelessly connected smart phone, awiredly/wirelessly connected personal computer, a wiredly/wirelesslyconnected PDA, a wiredly/wirelessly connected personal computer, and anearphone. The external input/output unit 213 may transmit datatransmitted from such an external appliance to respective componentswithin the smart phone 200, or transmit internal data of the smart phone200 to the external appliance.

The GPS receiver unit 214 receives GPS signals transmitted from GPSsatellites ST1 to STn according to an instruction of the main controlunit 220 and executes a positioning calculation processing based on thereceived GPS signals, thereby detecting a location including thelatitude, the longitude, and the elevation of the smart phone 200. Whenthe GPS receiver unit 214 is capable of acquiring position informationfrom the wireless communication unit 210 or the external input/outputunit 213 (e.g., wireless LAN), the GPS receiver unit 214 may detect alocation using the position information therefrom.

The motion sensor unit 215 includes, for example, a 3-axis accelerationsensor so as to detect a physical movement of the smart phone 200according to an instruction of the main control unit 220. The movementdirection or acceleration of the smart phone 200 is detected bydetecting a physical movement of the smart phone 200. The detectedresult is output to the main control unit 220.

The power source unit 216 supplies a power accumulated in a battery (notillustrated) to each part of the smart phone 200 according to aninstruction of the main control unit 220.

The main control unit 220 includes a microprocessor so as to operateaccording to control programs or control data stored in the storage unit212 to totally control each part of the smart phone 200. In addition,the main control unit 220 has a mobile communication control functionand an application processing function to control each part of acommunication system via the wireless communication unit 210 in order toperform voice communication or data communication.

The application processing function is implemented as the main controlunit 220 operates according to application software stored in thestorage unit 212. Examples of application processing function include aninfrared communication function for data communication with acounterpart appliance by controlling the external input/output unit 213,an electronic mail function for transmission/reception of e-mails, and aweb browsing function for reading a web page.

In addition, the main control unit 220 has, for example, an imageprocessing function of displaying an image on the display input unit 204based on image data (still image or moving image data) such as receiveddata or downloaded streaming data. The image processing function refersto a function performed by the main control unit 220 to decode the imagedata, to perform an image processing based on the decoded result, and todisplay the image on the display input unit 204.

In addition, the main control unit 220 executes a display control forthe display panel 202 and operating a detection control for detectingthe user's operation performed via the operating unit 207 and theoperating panel 203. With the execution of the display control, the maincontrol unit 220 displays a software key such as an icon or a scroll barfor starting application software, or a window for writing an e-mail.Meanwhile, the scroll bar refers to a software key for receiving aninstruction to move a display portion of a large image that does notwholly enter the display region of the display panel 202.

In addition, through the execution of the operating detection control,the main control unit 220 detects the user's operation performed via theoperating unit 207, or receives an operation performed on an icon viathe operating panel 203 or an input of a character string on an inputbox of the window, or receives a scroll demand for a display image viathe scroll bar.

In addition, through the execution of the operating detection control,the main control unit 220 has a touch panel control function ofdetermining whether an operating position for the operating panel 203 isan overlapping portion (display region) superposed on the display panel202 or any other non-overlapping outer edge portion (non-display region)not superposed on the display panel 202, and controlling a displayposition of a sensitive region of the operating panel 203 or a softwarekey.

In addition, the main control unit 220 may detect a gesture operationwith respect to the operating panel 203 and execute a preset functionaccording to the detected gesture operation. The gesture operation meansan operation of drawing a path with, for example, a finger, an operationof simultaneously designating a plurality of positions, or an operationof combining the operations so as to draw a path for at least one of thepositions, rather than a conventional simple touch operation.

The camera unit 208 includes components, other than the external memorycontrol unit 20, the recording medium 21, the display control unit 22,the display unit 23, and the operating unit 14 of the digital cameraillustrated in FIG. 1. Picked-up image data produced by the camera unit208 may be stored in the storage unit 212, or may be output via theinput/output unit 213 or the wireless communication unit 210. Asillustrated in FIG. 8, in the smart phone 200, while the camera unit 208is mounted to the same surface as the display input unit 204, themounting position of the camera unit 208 is not limited thereto and maybe mounted on the rear surface of the display input unit 204.

The camera unit 208 may be used in various functions of the smart phone200. For example, an image obtained by the camera unit 208 may bedisplayed on the display panel 202, or an image of the camera unit 208may be used as one operating input of the operating panel 203. Inaddition, when the GPS receiver unit 214 detects a position, theposition may be detected with reference to an image from the camera unit208. In addition, with reference to an image from the camera unit 208,the optical axis direction of the camera unit 208 of the smart phone 200may be determined or the current use environment may be determined withor without using a 3-axis acceleration sensor. Of course, an image fromthe camera unit 208 may be used in application software.

In addition, for example, position information obtained by the GPSreceiver unit 214, voice information obtained by the microphone 206(which may be turned into text information through a voice to textconversion by, for example, the main control unit), and postureinformation acquired by the motion sensor unit 215 may be added to imagedata including still images or moving images and then stored in thestorage unit 212 or output via the input/output unit 213 or the wirelesscommunication unit 210.

Even in the smart phone 200 having the above-described configuration,when the contrast AF processing unit 19 of FIG. 1 is installed to thecamera unit 208, high speed and high precision AF is enabled.

As described above, the following items are disclosed in the descriptionof the embodiments.

It is disclosed an imaging apparatus including: a focus lens configuredto be movable in an optical axis direction; an imaging elementconfigured to image an object via the focus lens; an evaluated valuecalculation unit configured to calculate an evaluated value for focusingusing a picked-up image signal obtained through imaging by the imagingelement at every position of the focus lens while moving the focus lens;a sharpness calculation unit configured to calculate a sharpness in avicinity of a maximal point of an evaluated value curve, whichrepresents relationship between a position of the focus lens and theevaluated value, using at least three evaluated values calculated by theevaluated value calculation unit and position information of the focuslens corresponding to each of the three evaluated values; a focusingposition calculation unit configured to select, according to at leastthe sharpness calculated by the sharpness calculation unit, one ofplural kinds of calculation methods using the three evaluated values andthe position information of the focus lens corresponding to each of thethree evaluated values, and to calculate the position of the focus lenscorresponding to the maximal point of the evaluated value curve as afocusing position using the selected calculation method; and a focusingcontrol unit configured to perform a focusing control to move the focuslens to the focusing position, in which the calculation methods include:a first calculation method for calculating a second or higher degreefunction representing the evaluated value curve using the threeevaluated values and the position information of the focus lenscorresponding to each of the three evaluated values, and calculating thefocusing position using the second or higher degree function; and asecond calculation method for calculating a first degree function usingthe three evaluated values and the position information of the focuslens corresponding to each of the three evaluated values and calculatingthe focusing position using the first degree function, and in which thethree evaluated values include a maximum value among the evaluatedvalues calculated by the evaluated value calculation unit and evaluatedvalues calculated in relation with positions in front and rear of theposition of the focus lens corresponding to the maximum value.

The imaging apparatus may have a configuration, in which the focusingposition calculation unit selects one of the calculation methodsaccording to the sharpness and a noise quantity included in theevaluated values.

The imaging apparatus may have a configuration, in which, in a casewhere the sharpness exceeds a first critical value and the noisequantity is equal to or less than a second critical value, the focusingposition calculation unit selects the second calculation method, in acase where the sharpness exceeds the first critical value and the noisequantity exceeds the second critical value, the focusing positioncalculation unit selects the first calculation method, and in a casewhere the sharpness is equal to or less than the first critical value,the focusing position calculation unit selects the first calculationmethod.

The imaging apparatus may have a configuration, in which, in a casewhere the sharpness exceeds a critical value, the focusing positioncalculation unit selects the second calculation method and in a casewhere the sharpness is equal to or less than the critical value, thefocusing position calculation unit selects the first calculation method.

The imaging apparatus may have a configuration, in which, in a casewhere panning is being performed and a movement speed of the imagingapparatus or a speed of a moving object included in the photographingobject exceeds a critical value, the focusing position calculation unitcalculates the focusing position using the three evaluated values, theposition information of the focus lens corresponding to each of thethree evaluated values, and a third or higher degree function,regardless of the sharpness.

The imaging apparatus may have a configuration, in which the imagingelement is not equipped with an optical low-pass filter.

It is disclosed a focusing control method by an imaging apparatus havingan imaging element configured to perform imaging of an object via afocus lens that is movable in an optical axis direction, the methodincluding: an evaluated value calculation step of calculating anevaluated value for focusing using a picked-up image signal obtainedthrough imaging by the imaging element at every position of the focuslens while moving the focus lens; a sharpness calculation step ofcalculating a sharpness in a vicinity of a maximal point of an evaluatedvalue curve, which represents relationship between a position of thefocus lens and the evaluated value, using at least three evaluatedvalues calculated by the evaluated value calculation unit and positioninformation of the focus lens corresponding to each of the threeevaluated values; a focusing position calculation step of selecting,according to at least the sharpness calculated by the sharpnesscalculation unit, one of plural kinds of calculation methods using thethree evaluated values and the position information of the focus lenscorresponding to each of the three evaluated values, and calculating theposition of the focus lens corresponding to the maximal point of theevaluated value curve as a focusing position using the selectedcalculation method; and a focusing control step of performing a focusingcontrol to move the focus lens to the focusing position, in which thecalculation methods include: a first calculation method for calculatinga second or higher degree function representing the evaluated valuecurve using the three evaluated values and the position information ofthe focus lens corresponding to each of the three evaluated values, andcalculating the focusing position using the second or higher degreefunction; and a second calculation method for calculating a first degreefunction using the three evaluated values and the position informationof the focus lens corresponding to each of the three evaluated valuesand calculating the focusing position using the first degree function,and in which the three evaluated values include a maximum value amongthe evaluated values calculated by the evaluated value calculation unitand evaluated values calculated in relation with positions in front andrear of the position of the focus lens corresponding to the maximumvalue.

In particular, the disclosed imaging apparatus and the disclosedfocusing control method may be conveniently and effectively applied to adigital camera, for example.

What is claimed is:
 1. An imaging apparatus comprising: a focus lensconfigured to be movable in an optical axis direction; an imagingelement configured to image an object via the focus lens; an evaluatedvalue calculation unit configured to calculate an evaluated value forfocusing using a picked-up image signal obtained through imaging by theimaging element at every position of the focus lens while moving thefocus lens; a sharpness calculation unit configured to calculate asharpness in a vicinity of a maximal point of an evaluated value curve,which represents relationship between a position of the focus lens andthe evaluated value, using at least three evaluated values calculated bythe evaluated value calculation unit and position information of thefocus lens corresponding to each of the at least three evaluated values;a focusing position calculation unit configured to select, according toat least the sharpness calculated by the sharpness calculation unit, oneof plural kinds of calculation methods using the at least threeevaluated values and the position information of the focus lenscorresponding to each of the at least three evaluated values, and tocalculate the position of the focus lens corresponding to the maximalpoint of the evaluated value curve as a focusing position using theselected calculation method; a focusing control unit configured toperform a focusing control to move the focus lens to the focusingposition; and at least one processor configured to function as theevaluated value calculation unit, the sharpness calculation unit, thefocusing position calculation unit, and the focusing control unit. 2.The imaging apparatus according to claim 1, wherein the plural kind ofcalculation methods include a first calculation method for calculating asecond or higher degree function representing the evaluated value curveusing the at least three evaluated values and the position informationof the focus lens corresponding to each of the at least three evaluatedvalues, and calculating the focusing position using the second or higherdegree function.
 3. The imaging apparatus according to claim 1, whereinthe plural kind of calculation methods include a second calculationmethod for calculating a first degree function using the at least threeevaluated values and the position information of the focus lenscorresponding to each of the at least three evaluated values andcalculating the focusing position using the first degree function. 4.The imaging apparatus according to claim 1, wherein the at least threeevaluated values include a maximum value among the evaluated valuescalculated by the evaluated value calculation unit and evaluated valuescalculated in relation with positions in front and rear of the positionof the focus lens corresponding to the maximum value.
 5. The imagingapparatus according to claim 1, wherein the focusing positioncalculation unit selects one of the plural kind of calculation methodsaccording to the sharpness and a noise quantity included in theevaluated values.
 6. The imaging apparatus according to claim 1,wherein, in a case where panning is being performed and a movement speedof the imaging apparatus or a speed of a moving object included in aphotographing object exceeds a critical value, the focusing positioncalculation unit calculates the focusing position using the at leastthree evaluated values, the position information of the focus lenscorresponding to each of the at least three evaluated values, and athird or higher degree function, regardless of the sharpness.
 7. Theimaging apparatus according to claim 1, wherein the imaging element isnot equipped with an optical low-pass filter.
 8. A focusing controlmethod by an imaging apparatus having an imaging element configured toperform imaging of an object via a focus lens that is movable in anoptical axis direction, the focusing control method comprising: anevaluated value calculation step of calculating an evaluated value forfocusing using a picked-up image signal obtained through imaging by theimaging element at every position of the focus lens while moving thefocus lens; a sharpness calculation step of calculating a sharpness in avicinity of a maximal point of an evaluated value curve, whichrepresents relationship between a position of the focus lens and theevaluated value, using at least three evaluated values calculated by theevaluated value calculation step and position information of the focuslens corresponding to each of the at least three evaluated values; afocusing position calculation step of selecting, according to at leastthe sharpness calculated by the sharpness calculation unit, one ofplural kinds of calculation methods using the at least three evaluatedvalues and the position information of the focus lens corresponding toeach of the at least three evaluated values, and calculating theposition of the focus lens corresponding to the maximal point of theevaluated value curve as a focusing position using the selectedcalculation method; and a focusing control step of performing a focusingcontrol to move the focus lens to the focusing position.
 9. The focusingcontrol method according to claim 8, wherein the plural kind ofcalculation methods includes a first calculation method for calculatinga second or higher degree function representing the evaluated valuecurve using the at least three evaluated values and the positioninformation of the focus lens corresponding to each of the at leastthree evaluated values, and calculating the focusing position using thesecond or higher degree function.
 10. The focusing control methodaccording to claim 8, wherein the plural kind of calculation methodsincludes a second calculation method for calculating a first degreefunction using the at least three evaluated values and the positioninformation of the focus lens corresponding to each of the at leastthree evaluated values and calculating the focusing position using thefirst degree function.
 11. The focusing control method according toclaim 8, wherein the at least three evaluated values include a maximumvalue among the evaluated values calculated by the evaluated valuecalculation step and evaluated values calculated in relation withpositions in front and rear of the position of the focus lenscorresponding to the maximum value.